The present invention is directed to bicycles and, more particularly, to various features of a shift control device for a bicycle transmission.
Conventional shift control devices for bicycle transmissions typically include a lever or twist grip that is rotated in two directions. One rotational direction is used to upshift the bicycle transmission, and the other rotational direction is used to downshift the bicycle transmission. The bicycle transmission moves by an amount proportional to the movement of the shift control device in either direction.
More advanced shift control devices use ratchet and pawl mechanisms and two levers to control a wire winding member that controls the bicycle transmission. An example of such a shift control device is shown in U.S. Pat. No. 5,400,675. More specifically, a downshift lever is used to operate the wire winding member in a downshifting direction, and an upshift lever is used to operate the wire winding member in an upshifting direction. Pushing the downshift lever from a home position to a downshift position moves the wire winding member in a downshifting direction by a proportional amount until a downshift ratchet and pawl mechanism maintains the wire winding member in the newly selected position, which may correspond to up to speed steps. As a result, moving the downshift lever from the downshift position back to the home position does not have any effect on the position of the wire winding member (except for play in the components). Pushing the upshift lever from a home position to an upshift position moves the wire winding member in an upshifting direction (opposite the downshifting direction) through a two-stage process. In the first stage, the upshift lever is pushed from the home position to the upshift position, and the wire winding member moves in the upshifting direction by an amount determined by the releasing action of an upshift ratchet and pawl mechanism. In the second stage, the upshift lever is allowed to move from the upshift position back to the home position. In this case, the upshift ratchet and pawl mechanism allows the wire winding member to move the remaining amount required by the upshifting operation and thereafter stops the rotation of the wire winding member to complete the shift. However, only one speed step change may be achieved with such a construction.
In any event, known dual-lever shift control devices have the ability to operate the bicycle transmission through multiple speed steps in either the upshifting direction or the downshifting direction using a single operation of one of the levers. However, such an operation is not possible for both levers.